Safe load control device for cranes



March 5, 1968 Y J. L. GROVE 3,371,800

SAFE LOAD CONTROL DEVICE FOR GRANES Filed July 21, 1966 I 4 Sheets-Sheet 1 FIG I IN VEN TOR.

6% JOHN L.GROVE ATTORNEY March 5, 1968 J. L. GROVE 3,371,800

SAFE LOAD CONTROL DEVICE FOR CRANES Filed July 21. 1966 4 Sheets-Sheet z .I\ swi ATTORNEY March 5, 1968 J, GROVE 3,371,800

SAFE LOAD CONTROL DEVICE FOR CRANES Filed July 21, 1966 4 Sheets-Sheet 5 VALVES SOLENOID FLY TELE/ MID T'E LE INVENTOR.

JOHN L. GROVE March 5, 1968 J. L. GROVE SAFE LOAD CONTROL DEVICE FOR CRANES Filed July 21, 1 966 4 Sheets-Sheet 4 mmwo m o 8 ATTORNEY M rl v M m M W W B M n m 9 w H m M m w. A m a H F H m H H W u a 1|. I= /mm mar mm 9 X1? W X .|1l |||l|| {IL OJ .1 ll1-|-W F111 {ML 2 $3; SE28 :32; Q22 A I] .-i J w A m1 Nw g 8 N l M. TN. i m ii 22 58m 5i fi u E: 5 5%; 3% M 0 Wm A S in r| IL II Pl $35 2233 @QE 7 y.

United States Patent Ofiice 3,371,800 SAFE LOAD CONTROL DEVICE FOR CRANES John L. Grove, Greencastle, Pa., assignor to Grove Manufacturing Co., Shady Grove, Pa., a corporation of Pennsylvania Filed July 21, 1966, Ser. No. 566,856 10 Claims. (Cl. 21239) ABSTRACT OF THE DISCLOSURE An overload preventive control device for cranes of the stationary and/r mobile types, the booms of which are pivotally raised and lowered in vertical planes, by means of extensible hydraulic motor or ram means, in cluding a pressure actuated switch responsive to the arcuate movements of the extensible lift ram, and the fluid pressure within said ram to calculate the crane tipping moment and render inoperative selected. operations of the crane.

Background of the invention In angularly movable booms adapted to lift a load by means of a winch controlled cable depending from the outer end of the boom, when the moment of force exerted by the load being lifted approaches a value greater than the moment of resistance exerted by the stationary structure or mobile vehicle supporting the boom, the boom and supporting structure is subject to tilting or pitching which can result in injury to the boom operator and other workers, and damage to the'boom and supporting structure. When the boom is connected to a stationary supporting structure, in such a manner that the supporting structure is not susceptible to tilting or pitching, then the boom is susceptible to bending when the moment of force exerted by the load thereon approaches a value greater than the designed bending strength of the boom. This could result in costly damage of the boom structure.

The value of the moment of force which causes the lifting boom to pitch or bend is commonly referred to as the pitching or bending moment. For purposes of ex planation in the present application, only pitching moment will be referred to, but it is to be understood that these references are also to be considered in certain circumstances as bending moments. The pitching moment of the lifting boom and supporting equipment, such as a mobile crane, is mainly dependent upon (1) the length of the moment arm as determined by the extended length and the angular position of the boom in the vertical plane, and (2) the moment of force exerted by the load being lifted relative to the different angular positions in the vertical plane through which the boom may be moved during the lifting or hoisting operations. Whenever one or a combination of these factors causes a load condition exceeding the pitching moment of the lifting boom apparatus, the portion of the hydraulic control system for the boom which enables the boom to be moved to an overload condition, or the pitching moment, is automatically locked out and the portion of the hydraulic control system which permits manipulation of the boom and lifting apparatus in directions to relieve the approaching overload condition are left in a condition of engagement so that the boom can be manipulated to prevent the pitching thereof.

In the past, overload safety control systems, generally of the type described herein, have utilized accurately machined camming surfaces connected on the boom structure and engaged by a pressure regulating device to determine the angular position of the boom in the vertical plane as set forth in 1) above, and separate pressure 3,371,800 Patented Mar. 5, 1968 regulating means connected to the load cable for sensing the load, as indicated in (2) above, such that the moment of force can be determined by a combination of the information obtained from both sensing means. Such an apparatus is shown in Patent 3,035,712, issued to R. Nowack on May 22, 1962. Such a system is relatively complicated and requires several sensing means, and in the past it has been found very difficult and expensive to machine the camming members attached to the booms so that accurate angular position information can be obtained therefrom.

The problem of determining the pitching moment becomes more difficult for a telescopic boom structure where the length of the boom is variable, such that there are a plurality of moment arm lengths for each particu lar extended length of the telescopic boom as it is raised and lowered in the vertical plane. A system such as disclosed in the mentioned patent therefore is inapplicable to a variable length boom structure.

It is therefore an object of this invention to provide a safe load control device for extensible boom structures which are angularly movable in the vertical plane.

Another object of the invention is to provide a safe load control device for cranes which is relatively simple in construction, economical to manufacture, and which takes advantage of the natural camming action designed into booms which are angularly movable in the vertical plane.

A further object of the invention is to provide a construction of overload preventive device for hydraulically extensible telescopic cranes which upon approach of the boom to an overload condition automatically locks out those portions of the hydraulic control system which would manipulate the boom into the overload condition r and maintains those portions of the hydraulic control system in engagement by which the boom may be manipulated away from the overload condition.

Still a further object of the invention is to provide a construction of safe load control device for hydraulic cranes which is connected to and obtains both vertical attitude and lifting load information from the boom lift cylinders.

Other and further objects of the invention are set forth more fully in the specification hereinafter following and will become apparent to one skilled in the art when considering the specification with the accompanying drawings, in which:

FIGURE 1 is a side elevational view, with parts broken away, showing the safe load control device of the invention connected to the hydraulic lift cylinders of an extensible boom structure;

FIG. 2 is an enlarged perspective view of a fragmentary portion of FIG. 1, showing the manner in which the safe load control device is connected to a lift cylinder;

FIG. 3 is a side elevational view with parts broken away, and partly in section, of the pressure switch device of FIG. 2; Y

.FIG. 4 is an enlarged transverse sectional view taken substantially along line 44 of FIG. 3;

FIG. 5 is an electrical schematic diagram of the electrical control system controlled by the safe load control device; and

FIG. 6 is a hydraulic schematic diagram of the hydraulic control system of a rotatable, extensible, angularly adjustable hydraulic crane embodying the present invention.

Referring to the drawings in greater detail, an exten sible hydraulic boom is'shown in FIG. 1, comprised of a base section 1, a mid-section 2 telescoped therein and extendible from the base section by means of a fiuid motor or double acting hydraulic ram 4 (FIG. 6) con- 3 nected between sections 1 and 2, and an outer or fly boom section 3 telescoped within mid-section 2 and extendible therefrom by means of a double acting hydraulic pistoncylinder or ram 5 (FIG. 6) connected between sections 1 and 2. The boom is pivoted at 6 to a pair of spaced upstanding supports 7 connected to turntable 8 which is rotatably connected to base structure 9, such as a mobile vehicle chassis or a stationary structure for 360 continuous rotation. A pair of double acting elevation or lift fluid motors or piston-cylinders it) and 11 are pivotally connected between turntable 8 and base section 1 of the boom at 12 and 13 respectively for raising and lowering the boom to selected angular positions relative to pivot point 6 in the vertical plane. The lift cylinders and 11 are controlled by a hydraulic control system, as schematically illustrated in FIG. 6, through hydraulic fluid under pressure conducted through hydraulic lines 14 connected to the tops of the cylinders for lowering the boom, and hydraulic lines 15 connected to the bottoms of the cylinders for elevating the extendible boom.

A hydraulic winch 16 is connected to the upstanding supports 7 or the inner end of the boom for controlling hoist cable 17 extending along the top of the boom and over sheaves (not shown) in the nose assembly 18 into connection with a load as schematically illustrated in FIG. 1. From FIG. 1 it can be appreciated that when the boom sections are fully extended from the retracted horizontal position, shown in full lines in FIG. 1, the moment arm of the boom is the longest and the moment of force exerted by a particular load connected to the end of cable 17 in this position is a maximum. As the boom is raised to its maximum elevation, as indicated in dotted lines in FIG. 1, the moment of force exerted by the load and the length of the moment arm decrease and are at a minimum for a particular load, when the boom is fully retracted in the elevated position. Thus, elevating the boom and/ or retracting the telescopic boom sections, decreases the moment of force exerted by a load, and extending the boom sections and/or lowering the boom increases the moment of force exerted by the load being lifted. The moment of force exerted by a load can also be decreased by lowering the load on the cable with winch 16 to thus unload the boom.

According to the invention, a hydraulic pressure switch 19 is connected in stationary relation to a portion of the turntable assembly, such as turntable 8, through mounting plate 20 and bracket 21. Pressure switch 19, for example, may be a modified Bulletin 836 Style T Pressure Switch manufactured by Allen-Bradley Co., Milwaukee, Wisconsin. This pressure switch is well known in the a t and as shown in FIGS. 3 and 4 comprises a sealed piston housing 22 extending from one end of main housing 23, and carrying a reciprocating piston therein having a rod 24 extending into the main housing. The inner end of rod 24 extends into the bore 25 of a plunger member 26 for axial movement relative thereto, with the bifurcated end 27 of movable plunger 26 extending from plunger housing 28 connected to the opposite side of main housing '23 from piston housing 22. A compression spring 29 is disposed about rod 24 and plunger member 26 interior of the housing 23 and is connected between seat 30 connected for movement with plunger 26 and floating seat 31 disposed about rod 24 and normally biased into abutment with outstanding boss 32 interior of housing 23. Piston rod 24 carries an enlarged diameter portion 33 outwardly of floating seat 31 which is adapted to move into contact with seat 31 as piston rod 24 is moved inwardly. Normally open microswitch 34, having a switch operating head 35, is connected adjacent members 24 and 26 with the head 35 thereof connected through pivoted spring biased linkage 36 in abutting contact at 37 through its bifurcated end 38 with floating seat 31. This linkage arrangement is all part of the standard switch structure with the only modification of the switch structure being the outward extension of plunger 26 extending through housing 28 and providing a bifurcated end 27 thereon for selected axial movement of the plunger. In the standard switch structure, plunger member 26 terminates in a range adjustment and lock nut assembly just outside main housing 23 in the position of plunger housing 28 by which a selected axial locked adjustment of plunger 26 is provided as compared with a variable adjustment of plunger 26 as in the present modified construction.

A hydraulic line 39 is connected at one end to the outer end of piston housing 22, FIGS. 1, 2, 3 and 6, and at the other end is disposed in fluid connection with the bottoms of lift cylinders 10 and 11 along with hydraulic lines 15, thereby conveying fluid under pressure from the bottom of the lift cylinders into piston housing 22 to axially move the piston and rod 24 therein against the bias of spring 29.

The bifurcated end 27 of plunger member 26 is connected through a linkage means, indicated generally at 40, to the cylinder casing of one of the elevation pistoncylinders such as cylinder 10. Linkage means 40 comprises an arm 41 pivoted at 42 to a bifurcated bracket 43 connected to mounting plate 20 with arm 41 pivotally connected at one end to the bifurcated end 27 of plunger member 26 and pivotally connected on its opposite end at 44 to an adjustable arm 45 which in turn is pivotally connected on its opposite end to a bracket 46 rigidly connected to the outer cylinder wall of lift fluid motor 10. As the boom is elevated by the lift fluid motors 10 and 11, these fluid motors during their extending and lifting operations, as shown in FIG. 1 in dotted lines, pivot clockwise in a predetermined are about their pivot connections 12 with the turntable to provide a natural carnming action, that is, a predetermined rotatable movement that is dependent upon or proportional to the angular elevation of the boom. As fluid motor 10 moves to the dotted position in FIG. 1, adjustable arm 45 is pulled in the same clockwise direction, causing arm 41 to pivot about point 42 and move plunger member 26 somewhat axially inwardly of main housing 23 of the main pressure switch. As plunger 26 moves inwardly, seat 30 carried thereby also moves inwardly placing spring 29 in a more compressed state. In this manner, boom elevation information is conveyed to the pressure switch, creating a greater spring biasing force within switch 19 through spring 29 which must be overcome by hydraulic presure acting upon the piston and piston rod 24 to move floating seat 31 axially inwardly of the switch causing movement of pivoted spring biased linkage 36 to relieve pressure from head 35 of microswitch 34 to thus close the microswitch. Since the hydraulic pressure acting upon the piston and rod 24 in piston housing 22 is the same as the hydraulic presure in the bottom of the lift fluid motors 10 and 11, this hydraulic pressure increases as the load on the boom hoist cable increases and/or as the length of the moment arm increases, which includes the length of the boom increasing as the boom is extended, because these factors result in greater force being exerted on the lift fluid motors 10 and 11. In this manner, load information is conveyed to the pressure switch and if the moment of force for a particular elevation of the boom approaches the pitching moment of the crane, portion 33 of piston rod 24 moves floating seat 31 inwardly against the compression force of spring 29 which is varied by the elevation attitude of the boom, to cause microswitch 34 to be closed by spring biased linkage 36. In the pressure switch 19 there is thus a differential action between the elevation information represented by inward movement of plunger 26 which increases the biasing force of compression spring 29, and the load information represented by the inward movement of rod 24 in the opposite axial direction against the biasing force of spring 29. The microswitch 34 is closed when the biasing force of spring 29 is overcome by the pressure acting on the piston in housing 22 of the pressure switch.

Referring to the electrical schematic diagram of FIG. 5, and the schematic hydraulic diagram of FIG. 6, when microswitch 34 is closed, due to an overload condition, relay 47 is energized causing its contacts 48 to close and supply DC voltage to hydraulic solenoid valves 49, 50, 51, 52 and 53 to energize the same and close the valves, operator warning light 54 to thus illuminate the same, and to energize an audio alarm 55 to produce an audio signal to warn the operator that an overload condition has been approached. The hydraulic solenoid valves comprise hydraulic valves connected into hydraulic fluid lines, which valves are electrically controlled by a solenoid. Reference numeral 49 represents the lift solenoid valve disposed in the hydraulic control circuit of lift fluid motors and 11. Solenoid valve 50 is disposed in the hydraulic control circuit of hydraulic ram 5, which extends and retracts the boom fly-section. Solenoid valve 51 is connected in the hydraulic control circuit of hydraulic ram 4 which extends and retracts the boom midsection 2 and winch solenoid valve 52 and winch booster solenoid valve 53 are connected in the hydraulic control circuit of hydraulic winch 16 which controls the raising and lowering of hoist cable 17. The hydraulic control circuit of FIG. 6 is generally conventional except for the addition of the solenoid valves 4953, and for this reason will not be described in great detail as this is believed unnecessary to a full understanding of the invention. Portions of the complete hydraulic control circuit have been omitted for clarity. The manual control valves, indicated in FIG. 6, are the operators manual lever controlled crane-manipulating valves located in the operators compartment or at the operator station. The main control valves pertinent to the present invention are main winch control valve 56, winch booster control valve 57, lift cylinders control valve 58, lift booster control valve 59, telescopic mid-section control valve 60 and telescopic fly-section control valve 61.

When solenoid valves 49-53 are energized, thus closing the valves to block fluid flow in the respective circuits, the operations of lifting with the winch 16 extending the boom sections 2 and/or 3 and lowering the boom by means of liftcylinders 10 and 11 are locked out. Solenoid valves 49-53 are each provided with a reverse flow bypass valve 62 to provide free flow of hydraulic fluid in the respective circuits in the opposite direction to thus allow the following hydraulic circuit operations: lifting the boom with lift cylinders 10 and 11 (this reduces the length of the moment arm); retracting boom mid-section 2 and/ or boom fly-section 3 by means of hydraulic rams 4 and 5, respectively (this reduces the length of the moment arm); and lowering the load on hoist cable 17 by means of winch 16 to remove the load from the boom. Raising the boom, or retracting the boom to decrease its overall length, decreases the hydraulic pressure in the bottom end of the lift cylinders 10 and 11 because the moment of force is decreased and the boom has been manipulated away from the unsafe condition. This decrease in the hydraulic pressure in the bottom of the lift cylinders causes piston rod 24 to move outwardly of pressure switch housing 23, resulting in microswitch 34 being moved to the open position, FIGS. 4 and 5, to extinguish warning light 54, cut ofl audio alarm 55 and de-energize solenoid valves 49-53 to again permit flow in the normal fluid circuits so that the operations of lifting with the winch, extending the boom, and lowering the boom, can again be performed.

By way of example, in normal operation, when lowering the boom the hydraulic fluid flow is from the hydraulic pump supply 63 through manual lift control valve 58, hydraulic lines 64, 65 and 14 to the tops of lift fluid motors 10 and 11, from the bottoms of these fluid motors through hydraulic lines 15, 66 through operator holding valve 67, hydraulic line 68, solenoid valve 49 and hydraulic lines 69 and 70, back to manual control valve 58. When pressure switch 19 is actuated and microswitch 34 is closed to energize and close lift solenoid valve 49 the hydraulic lifting circuit is interrupted and further manipulation of lift control valve 58 or lift booster control valve 59, which is connected in parallel with valve 58, will not allow further lowering of the boom. However, operation of either the double acting lift control valves 58 or 59, in the opposite direction, to raise the boom, will cause fluid flow along the following circuit, to perform this operation: from control valve 58 hydraulic fluid under pressure from the pump is supplied over hydraulic lines 70, 69 through reverse flow bypass valves 62, hydraulic lines 68, operator holding valve 67, hydraulic lines 66 and 15 to the bottoms of lift cylinders 10 and 11 to move the pistons therein upwardly to raise the boom, with fluid from the tops of the cylinders flowing through hydraulic lines 14, 65 and 64, back to the manual lift control valve 58 and to the fluid reservoir. From this example it can be seen how operation of the fluid circuit in one direction is locked out by the solenoid valve 49, while the fluid circuit in the opposite direction is maintained in operating condition by means of the reverse flow valve 62.

In like manner, the operating circuits for extending and retracting the mid-section telescopic cylinder 4, the fly-section telescopic cylinder 5 and the circuit for operating hydraulic winch 16 to lower and retract hoist cable 17 thereon can be traced in FIG. 6, as these circuits operate in the same manner as the hydraulic circuit for the lift cylinders 10 and 11, set forth above.

Whenever pressure switch 19 is operated to lock out the operations of lifting a load any further with winch 16, extending the bottom sections and lowering the boom, as soon as the boom is unloaded by lowering the load with the winch, or as soon as the boom is raised or retracted, to decrease the moment of force exerted by the load, the differential action between piston rod 24 and plunger 26 in the pressure switch will result in these members moving axially away from each other, or one of these members to move axially outwardly relative to the other, causing spring biased linkage 36 in the switch to depress switch operating head 35, allowing microswitch 34 to return to its normal open position to thus return all of the fluid circuits to their normal operative state.

While the invention has been shown and described in certain preferred embodiments, it is realized that modifications can be made without departing from the spirit of the invention, and it is to be understood that no limitations upon the invention are intended other than those imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A safe load control device for preventing the overloading and tipping of material-handling apparatus of the type comprising a boom pivotally connected on a supporting structure, and extensible fluid motor means connected between the boom and supporting structure for angularly moving the boom in the vertical plane, said control device comprising pressure actuated switch means having a first input means including a first movable member responsive to fluid under pressure and a second input means including a second movable member responsive to mechanical movement, said first and second movable members movable relative to each other, electrical contacts operatively connected to said first and second movable members for actuation thereby, first means connecting said first input means to said extensible fluid motor means for response to the pressure of the fluid therein corresponding to the loading of said boom, second means operatively connecting said second input means to said extensible fluid motor means for response to arcuate positions of said extensible fluid motor means corresponding to angular positions of said boom in the vertical plane, said first and second movable members of said pressure actuated switch means responsive to sense an overload moment of force on said apparatus when moved to predetermined relative positions to actuate said electrical contacts, and means perated by said electrical contacts to render said extensible fluid motor means inoperative to lower said boom.

2. A safe load control device as set forth in claim 1 in which said extensible fluid motor means comprise hydraulic cylinders with upwardly extending piston members, and said first means connected to the bottom portions of said hydraulic cylinders.

3. A safe load control device as set forth in claim l in which said first input means and said first movable member comprises a piston-cylinder assembly, and said first means comprises a fluid connection between said pistoncylinder assembly, and the fluid in said extensible fluid motor means.

4. A safe load control device as set forth in claim 1 in which said second movable member is axially movable and said second means comprises a pivoted linkage arm assembly pivotally connected to said second movable member.

5. A safe load control device as set forth in claim 4 in which said extensible fluid motor means comprise at least one hydraulic piston-cylinder unit, and said linkage arm assembly pivotally connected to the cylinder of said unit.

6. A safe load control device as set forth in claim 4 in which said linkage arm assembly includes a lever arm pivotally connected at one end to said second movable member of said second input means and at the opposite end to said extensible fluid motor means, and a pivot connection between said lever arm intermediate the said end pivot connection thereof and said supporting structure.

7. A safe load control device as set forth in claim 1, in which said means includes fluid control circuit means connected for extending and retracting said extensible fluid motor means, electrical control valve means connected in said fluid control circuit means, reverse flow valve means connected across said electrical control valve means, said electrical control valve means connected for control by said electrical contacts of said pressure actuated switch and responsive to interrupt said fluid control circuit means when said electrical contacts of said pressure actuated switch are actuated on sensing an overload force, whereby the fluid circuit means for retracting said fluid motor means through said electrical control valve means to lower said boom is rendered inoperative, while the fluid circuit means for extending said extensible fluid motor means through said reverse flow valve means to elevate said boom is maintained operative to manipulate said boom from the overload position.

8. A safe load control device as set forth in claim 7 in which said boom is comprised of at least two telescopic boom sections, a fluid motor unit connected between the said telescopic sections for relative extending and retracting movement of the sections, said means including second fluid control circuit means connected for extending and retracting said fluid motor unit, second electrical control valve means connected in said second fluid control circuit means, second reverse flow valve means connected across said second electrical control valve means, said second electrical control valve means connected for control by said electrical contacts of said pressure actuated switch and responsive to interrupt said second fluid control circuit means when said pressure actuated switch senses an overload moment to actuate said electrical contacts, whereby the second fluid circuit means for extending said fluid motor unit to extend said telescopic boom sections is rendered inoperative, while the second fluid circuit means through said second reverse flow valve means for retracting said fluid motor unit to retract said boom sections is maintained operative so that the boom length can be reduced to decrease the loading moment.

9. A safe load control device as set forth in claim 1 including a hoist cable extending from the end of said boom for connection with a load, fluid winch means connected for retracting and extending said hoist cable, said means including fluid circuit means connected for control of said winch means, electrical control valve means connected in said fluid circuit means, reverse flow valve means connected across said electrical control valve means to bypass the same when said electrical control valve means is closed, said electrical control valve means connected for control by said electrical contacts of said pressure actuated switch and responsive to interrupt said fluid circuit means when said electrical contacts of said pressure actuated switch are actuated on sensing an overload moment on said boom, whereby said fluid circuit means for operating said winch to retract said cable and raise a load thereon is rendered inoperative, while the fluid circuit means for operating said winch to extend said cable and lower a load thereon to unload said boom is maintained operative through said reverse flow valve means.

10. A safe load control device as set forth in claim 1, and alarm means connected for energization by said electrical contacts of said pressure actuated switch means upon sensing an overload moment.

References Cited UNITED STATES PATENTS 3,265,220 8/1966 Knight 212-39 FOREIGN PATENTS 95,141 7/1960 Netherlands.

RICHARD E. AEGERTER, Primary Examiner.

EVON C. BLUNK, Examiner.

H. C. HORNSBY, Assistant Examiner. 

